Japanese Patent Application Laid-Open (JP-A) No. 2011-519774 describes a cap-free neck end for a fuel container including a double flap closure formed by an upper pivoting flap and a lower pivoting flap.
In a structure provided with only one flap in a filler pipe (filler neck) for refueling a fuel tank, for example, the seal state of the flap can be determined (whether or not the seal is abnormal) by depressurizing the fuel tank and detecting the change in the internal tank pressure over time.
However, in a structure provided with two flaps in the filler neck as described in the above publication, in cases in which the fuel tank has been depressurized, even if the seal of one flap is abnormal, if the seal of the other flap is normal then sometimes the internal tank pressure of the fuel tank lowers such that the flaps are determined to be normal overall.
Namely, in a structure provided with two flaps in a filler pipe, the seal state of the flaps cannot be determined simply by depressurizing the fuel tank and detecting the change in the internal tank pressure.
In consideration of the above, an object of the present disclosure is to determine whether the seal states of flaps are normal or abnormal in a structure including two flaps in a filler pipe.